Little tunny

Little tunny

The little tunny (Euthynnus alletteratus) is the most common tuna in the Atlantic Ocean. It is found in warm temperate and tropical waters of the Atlantic and the Mediterranean; in the western Atlantic, it ranges from Brazil to the New England states. It is found regularly in offshore and inshore waters, and is classified as a highly migratory species by UNCLOS.[1] Occurring in large schools and weighing up to 36 pounds, it is the smallest member of the tuna Scombridae family, and is one of the finest small game-fish in the Atlantic.

Commonly called false albacore or little tuna, it resembles the Atlantic bonito, skipjack tuna and species of mackerel.[2] The little tunny feeds primarily on pelagic fish. It is best identified by the dark spots appearing between its pectoral and ventral fins and "worm-like" markings on its back.[3] Commercially, the fish is used as bait for sharks and marlin due to its high oil content and hook retention. It is considered by many to be a trash fish because of its limited nutritional value; there have even been reports of ciguatera poisoning related to its consumption. However, the little tunny is commercially important in many locations including the West Indies. It is marketed fresh, dried, canned, smoked, and frozen. It is sought after as a sport fish due to its line stripping 40 miles per hour (64 km/h) runs and hard fighting ability when hooked. By trolling with lures near reefs, it can be caught on hook and line.[4]

Contents

Taxonomy

Constantine Samuel Rafinesque identified the little tunny in 1810 and gave the fish its current name: Euthynnus alletteratus. Synonyms for used for the name include E. alleteratus alleteratus, E. alliteratus, E. thunina, and E. alletteratus aurolitoralis.[5] The little tunny is not part of the Thunnus genus like many tuna, but it is part of the Thunninitribe.

Etymology

The genus Euthynnus is derived from the Ancient Greek: εὖ(eu) "good, well", and θύννος (thýnnos), "tunny-fish" – which is in turn derived from θύνω(thynō), "to rush; to dart".[6]

Physical description

The little tunny is small in body size compared to other tuna species. It has a compact and stream-lined body built to facilitate bursts of speed as well as endurance while swimming. Its torpedo-shaped, robust body is made for powerful swimming.[7] It has a large mouth with rigid jaws and a slightly protruding lower jaw, with a single row of small, inwardly-curved, cone-shaped teeth on the palatines.[8] Teeth are absent on the vomer, the small bone in the roof of the mouth,[9] and the tongue has two longitudinal ridges.[10]

A little tunny.

The snout is shorter than the rest of the head. The little tunny has a dorsal fin with 10 to 15 tall, descending spines, as well as a much smaller second dorsal fin followed by 8 finlets. At the base, the two dorsal fins are separated by a small interspace.[11] The anal fin has 11 to 15 slightly defined rays, and is followed by 7 finlets. The pectoral fins are short and do not reach the end of the first dorsal fin and are joined to the pelvic fins by interpelvic processes.[12] There are 37-45 gill rakers, bony projections off the gills, on the first arch. There are no scales on the body of the little tunny except along the lateral line and on the corselet: a thick band of scales circling the body.[13]

The coloration of the little tunny is typically metallic blue or blue-green with dark wavy stripes above the lateral line. These "worm-like" lines are within a well marked border that never extends farther forward than the middle of the first dorsal fin.[14] The belly is bright white with 3–7 dark, fingerprint-like spots around the pectoral and pelvic fins. The little tunny is commonly confused with the Atlantic bonito because of coloration, but the two fish differ in their color patterns and overall body size.

The little tunny's markings allow it to easily be distinguished from similar species. The little tunny is often confused with the skipjack tuna, the frigate tuna, the Atlantic bonito, and the bullet tuna. Close relatives also include the kawakawa and the black skipjack. The scattering of dark, fingerprint-like spots between the pectoral and pelvic fins cannot be found on any related Atlantic species. The first dorsal fin of the Atlantic bonito is also lower and sloping. Its lack of teeth on the vomer can set it apart from its close Pacific relatives, the kawakawa and the black skipjack. The dorsal fins of the bullet and frigate mackerel are set apart. Unlike the little tunny, the skipjack tuna lacks markings on the back and has broad, straight stripes on the underside.[15]

Little tunny reach a maximum weight of 12 kilograms (26 lb) in the Mediterranean, and averages about 7 kilograms (15 lb) through its entire range. The maximum fork length (distance from the tip of the snout to the fork of the tail) of the little tunny in the Mediterranean is about 100 centimetres (39 in) and in the Atlantic is about a 90 centimetres (35 in).[16] Average fork length for an adult fish throughout the entire range is about 85 centimetres (33 in) .[17] Some little tunnies may reach the length of 40 inches (100 cm) or more, but most commonly they are around 25 inches (64 cm). The largest little tunny on record is 48 inches (120 cm) and 36.5 pounds (17 kg).[18] Females reach sexual maturity at 10.6 to 14.6 inches (27–37 cm) in fork length length while males mature at approximately 15.7 inches (40 cm).[19]

Anatomy

The little tunny has some anatomical variations when compared to other species of Euthynnus. E. alletteratus lacks a swim bladder, like most other tuna, so it must constantly keep moving to stay afloat. The pectoral fins are crucial to the little tunny in maintaining its position in the water column. The little tunny's liver is very disproportionate, with the right lobe much longer than the left or middle lobes. The stomach of the little tunny is a long sac that stretches almost the entire length of its body. The intestinal tract is fairly short, coming from the left and right sides of the stomach, and extending without looping down the length of the tuna's body. The different sections are characterized by their diameter and color.[20] The ventral vertebral column of the little tunny has unique trelliswork, which is important to its family (Scombridae.) Divided haemapophyses, or parts of the vertebrate, forming a long canal enclose the large ventral blood vessel.[21]

Feeding habits

A school of little tunny feeding.

In coastal waters along the North American eastern seaboard, little tunny are carnivorous, and primarily feed on small fish and invertebrates that occur in schools. The diet of the Little Tunny consists mostly of fish, they particularly like the Atlantic Bigeye and largehead hairtail. Second to fish, the Little Tunny consumes a good deal of crustaceans, and lastly cephalopods and gastropods make up a small part of the Little Tunny's diet. Sardines, scad, and anchovies are common in the diet along with squid, stomatopods, and organisms from the diogenidae family. The diet of the fish is also relative to its size. A smaller fish's diet typically consists of clupeiform, and larvae, while the larger fish mostly eat maurolicus muelleri. The typical diet is very similar to that of the king mackerel because the fish are of a similar size and live in the same area of the water column.[2] It mostly feeds on pelagic fish. The little tunny is an opportunistic predator, feeding on crustaceans, clupeid fishes, squids, and tunicates. The Little Tunny's diet also responds to seasonal changes in food availability. It has been observed that the Little Tunny has nocturnal feeding habits, and are specialist feeders. It often feeds on herring and sardines in inshore waters near the surface of the water.[22] The little tunny commonly feeds in large schools because their primary food sources (small fish and the larval forms of crustaceans) are typically in schools as well.

The little tunny's habitat tends to be near-shore waters, much closer to shore than most other tunas. They live in and around inlets, points, jetties, and sandbars. All of these places are where bait fish like sardine and menhaden, both favorites of the little tunny, form large schools, which are very helpful to the little tunny's feeding style. While the little tunny is abundant in offshore ocean waters, it is unusual to find it in brackish water of estuaries. The very young will enter estuaries in South Africa.[24] The little tunny prefers relatively warm water, from 24° to 30° Celsius. The little tunny migrates south in the winter and fall, and northward in the spring, through coastal waters. It is not as migratory as other tuna species.[25]

The little tunny is typically a schooling species.[26] It lives in schools based primarily on fish size rather than species, so other members of the Scombridae family, like the Atlantic bonito, may be present. These schools cover areas up to 2 miles long. Little tunny that have not yet reached adulthood form tight schools offshore. Larger schools are more common offshore whereas smaller groups may wander far inshore.

Reproduction

Little tunny spawn in water that is at least 25 °C(77 °F) in the months of April through November in the Atlantic Ocean. The spawning season of the little tunny in the Mediterranean is generally between May and September, but the most intensive spawning occurs between July and August. The major spawning areas are offshore, in waters that are 100 to 130 feet deep. The females are prolific fish, and can release 1.75 million eggs, in multiple clutches over a mating season.[27] The eggs are fertilized in the water column after the males release sperm. The eggs are buoyant, spherical, transparent, and pelagic. A droplet of oil within the egg adds to its buoyancy. The diameter of the eggs can be anywhere from 0.8 mm to 1.1 mm, and they are light amber. Larvae are released 24 hours after fertilization and are approximately 3 mm in size. Pigmentation in the eyes appear 48 hours after hatching. The teeth and fins develop at sizes of 3.7–14 mm. Once the larvae are 14 mm to 174 mm long, they take on the adult appearance; the body becomes more elongated.[28] Studies have found that it takes approximately 3 years for the little tunny's gonads to reach sexual maturity. The average size of a sexually mature individual is 15 inches (38 cm) in fork length.[29]

Predators and parasites

Bony fish, Marlins, sea birds, sharks, and rays prey on the little tunny.[30] Other tunas, including conspecifics and yellowfin tuna (Thynnus albacares) are predators of the little tunny. Fish such as the dolphin fish (Coryphaena hippurus), wahoo (Acanthocybium solandri), Atlantic sailfish (Istiophorus albicans), swordfish (Xiphias gladius), and various sharks as well as other large marine carnivores all prey on the little tunny. Among those sharks is the whale shark, who feeds on the little tunny's recently spawned eggs. Seabirds prey on small little tunny.[31]

Parasites of the little tunny include the copepods Caligus bonito, Caligus coryphaenae, and Caligus productus, all found on the body surface as well as on the wall of the branchial cavities. Another copepod, Pseudocycnoides appendiculatus, has been documented as parasitic on the gill filaments. Other parasites include digenea (flukes), monogenea (gillworms), cestoda (tapeworms), and isopods.[32]

Fishing and preparation

As with many inshore gamefish like bluefish and striped bass, schools of little tunny are usually indicated by flocks of birds diving in coastal waters. Fishermen targeting them often troll bait, cast lures, and float fish. When trolling for Little Tunny, fishermen often use small lures baited with either mullet or ballyhoo or lures dressed with colored feathers. When float fishing, popular baits are Spot, Bluefish, or Pinfish. Popular lures include deadly dicks, maria jigs, and other slender-profiled, brightly-colored metal lures that can be cast far and retrieved quickly that imitate the small baitfish the little tunny are often feeding on. Some anglers use little tunny for strip bait to catch other species, but most fish are released as the Little Tunny is not commonly thought of as a food fish. There is little regulation of the fishery, no size or bag limits, and no closed season. The flesh of the Little Tunny is coarse in texture, strong in flavor, and dark in color if compared to bluefin or yellowfin tuna.[33]

In preparing Little Tunny for consumption, it should be bled and iced as soon as possible after being caught. There are many ways to eat the Little Tunny, such as Tuna Salad. To do this, the fillets are first baked, then chilled and flaked, then mixed in with the salad. Removing the dark strips of meats that extend the length of each fillet helps to reduce the naturally fishy flavor.[34] Another way to prepare the Little Tunny is first to bleed it, barbecue it in foil, remove the meat from the bone, and then let it chill overnight. Various seasonings can be used to enhance the flavor. Fresh steaks can be quiet good if seasoned with salt, pepper and lemon, and thinly sliced tunny makes good sashimi. It is commonly eaten as such in Japan.